The present invention relates to fastening parts made of composite material that are used in the after-bodies of aeroengines such as turbojets.
In order to reduce the weight of after-bodies, it is known to make one or more parts of an after-body, such as the exhaust cone and/or the primary nozzle, out of composite material instead of metal. Such parts present a coefficient of thermal expansion that is low compared with that of the metal exhaust casing of the engine on which they are to be mounted. In order to compensate for the differential expansion between such elements, the composite material parts are mounted on the metal casing by means of resiliently flexible fastener tabs that are generally made of refractory metal.
FIG. 5 shows a turbojet after-body as described in Document US 2011/203255. The after-body comprises an ejection or primary nozzle 10 and a central body or exhaust cone 20 (also known as a “plug”). The primary nozzle 10 and the exhaust cone 20 are made of CMC composite material which, in well-known manner, are made of fiber reinforcement made of (carbon or ceramic) refractory fibers and densified by a ceramic matrix, in particular a matrix of refractory carbide, nitride, or oxide.
The primary nozzle 10 is fastened on a first metal fastener ring 40 forming part of or designed to be fastened to the engine exhaust casing (not shown) by means of resiliently flexible fastener tabs 50. The exhaust cone 20 is fastened to a second metal fastener ring 60 likewise forming part of the exhaust casing by means of elastically deformable fastener tabs 70. The fastener tabs are made of a refractory material, such as, in particular, Inconel®, Hastelloy®, or Waspalloy®. Depending on the size and the weight of the CMC parts, the fastener tabs are dimensioned to provide mechanical strength to withstand both normal and limiting loads that correspond to maintaining radial and axial clearance between the CMC part and the metal part so as to make it possible to compensate for differential expansion and to damp vibration.
Nevertheless, fastening composite material parts on metal parts in that way presents certain drawbacks. Firstly, the metal fastener tabs represent a significant fraction of the total weight of the part, specifically about 30%. The use of fastener tabs of that type also makes it more complex to manage sealing with the casing. Finally, the cost of fabricating such fastener tabs is relatively high.